Catalytic process for removing sulfur dioxide from gas streams

ABSTRACT

This application describes a process for the catalytic reduction of sulfur dioxide in gas streams containing sulfur dioxide to elemental sulfur using a reducing gas such as hydrogen or, preferably, carbon monoxide, and a catalyst of the formula Ln 2  O 3  . Co 2  O 3 , where Ln is either Y or Gd.

FIELD OF THE INVENTION

This invention relates to the removal of sulfur dioxide from gas streamscontaining sulfur dioxide. More particularly, this invention relates tothe catalytic reduction of sulfur dioxide with a reducing gas,preferably carbon monoxide, to elemental sulfur in gas streamscontaining sulfur dioxide, such as flue or stack gases, gases resultingfrom oil or coal gasification which contain sulfur dioxide, smeltergases, etc.

BACKGROUND OF THE INVENTION

Sulfur dioxide is a constituent of many waste gases, such as, forexample, smelter gases, flue gases, off gases from chemicalmanufacturing processes, ore roaster gases, and stack gases from coal-and oil-burning furnaces and boilers. Contamination of the atmosphere bysulfur dioxide, whether present in dilute concentrations of 0.05 to 0.3volume percent as in power plant flue gases or in higher amounts of 5 to10 percent as in ore roaster gases, has been a public health problem formany years due to its irritating effect on the respiratory system, itsadverse affect on plant life, and its corrosive attack on many metals,fabrics and building materials. Millions of tons of sulfur dioxide areemitted into the atmosphere each year in The United States due tocombustion of fuel oil and coal; a major amount of such sulfur dioxidebeing produced in the generation of electric power.

Since the reduction of the sulfur dioxide content of stack gases is thekey to the production of useful energy from our abundant fuels (coal andhigh sulfur oil) in an environmentally acceptable manner, many methodshave been proposed, and are presently under study, for the removal ofsulfur dioxide from such gases. It is estimated that there are close to50 sulfur dioxide removal processes presently under investigation in theUnited States. While the processes appear technically feasible, theexpense of the sulfur dioxide removal is substantial. Some of the morecommon processes involve scrubbing of the stack gas and precipitation ofthe sulphur dioxide with limestone as calcium sulfite or, followingoxidation, as calcium sulfate. Scrubbing of the very large effluent gasquantities, as well as collection and disposal of the solid precipitatefrom the scrubbing liquid, are expensive.

An inherently less expensive method for removing the sulfur dioxide isbased on the catalytic reduction thereof with carbon monoxide or someother reductant. Neither scrubbing of a gas by a liquid nor theseparation of a solid from a liquid are required in this method. Thismethod has been tried with many different catalysts but, to date, to thebest Applicant's knowledge, such methods have one or more of three majordifficulties. Initially, burners, such as those operated by electricalpower generation, run on fuel mixes with excess air or "lean fuelmixes". This is done to prevent the formation of explosive carbon dustand to derive more energy from the fuel. As a result of the use of thelean fuel mix, the stack gas is rich in oxygen. This oxygen poisonedmany of the catalysts tried in the past, thus killing the catalyticactivity thereof and reducing the overall effectiveness of the reductionprocess. Secondly, certain of the catalysts utilized catalyzed thereduction of water by carbon monoxide to form carbon dioxide andhydrogen, or catalyzed the reaction of water and sulfur to hydrogensulfide and oxygen. Hydrogen reacts with sulfur to form hydrogen sulfideat temperatures as low as about 200°C, and, thusly, in either case, thesulfur dioxide is converted into another toxic material. Thirdly,certain of the non-specific catalysts catalyzed the oxidation of carbonmonoxide to sulfur to form carbonyl sulfide, another highly toxic gas.These difficulties arise because of the non-specific nature of thecatalytic material.

OBJECTS OF THE INVENTION

It is, therefore, the primary object of this invention to define a novelprocess for the removal of sulfur dioxide from gas streams containingsulfur dioxide.

It is a further object of this invention to provide a process for thecatalytic reduction of sulfur dioxide to elemental sulfur.

It is a further object of this invention to provide a process for thecatalytic reduction of sulfur dioxide in gas streams containing sulfurdioxide to elemental sulfur using specific catalytic compositions whichare not subject to poisoning by oxygen or water, and are less subject tothe aforementioned deficiencies.

It is a further object of this invention to provide a process for thecatalytic reduction of sulfur dioxide by a reducing gas to elementalsulfur, said process being sufficiently specific to operate with leanfuel mixtures while forming environmentally acceptable levels of sulfurdioxide, hydrogen sulfide, or carbonyl sulfide.

These and still further objects, advantages and features of the presentinvention will become apparent upon consideration of the followingdetailed disclosure.

SUMMARY OF THE INVENTION

These and still further objects, features and advantages of the presentinvention are achieved, in accordance therewith, by utilizing acomposition represented by the formula Ln₂ O₃ . Co₂ O₃, where Ln iseither Y or Gd, as the catalyst in the catalytic reduction of sulfurdioxide with a reducing gas, such as hydrogen or, preferably, carbonmonoxide, in sulfur-dioxide containing gas streams to elemental sulfur.Catalysts having a 1 : 1 ratio of cobalt oxide to either Y₂ O₃ or Gd₂ O₃are preferred since maximum catalytic conversion efficiencies areobtainable therewith. Other ratios, if reasonably close to preferred 1 :1 ratio, are suitable since the desired catalytic conversion toelemental sulfur is effected.

In its broadest aspects, the process of the present invention isdirected to the removal of sulfur dioxide from any sulfurdioxide-containing gas stream where the above-identified catalyst isused and a reducing gas, such as hydrogen or, preferably, carbonmonoxide, is added to, or present in sufficient quantities in, thesulfur dioxide-containing gas stream to within about 35 15%, generallyabout 35 10%, of the stoichiometric amount required for completereduction of all sulfur dioxide present to elemental sulfur. If theamount of reducing gas in the stream is sufficient, no further amountneed be added thereto. However, quantities of the reducing gas can beadded, or generated in situ, as necessary to provide the desired amountof reductants, relative to oxidants, in the gas stream.

The first, and presently considered to be the most important aspect ofthe present invention is a process directed to the removal of sulfurdioxide from sulfur dioxide-containing flue or stack gases, especiallythose resulting from coal-burning processes, oil burning processes, orany other process which produces sulfur dioxide in the tail gas. Ofspecial interest is the particularly severe case of a stack gasresulting from a coal-burning operation where the stack gas contains flyash (to the extent not removed by precipitation) and generally has acomposition of about 0.32% SO₂, 3.2% O₂, 15% CO₂, 7.6% H₂ D, 0.12%nitrogen oxide, balance nitrogen, i.e., where the O₂ /SO₂ ratio is about10:1 and the H₂ O content is very high (which could lead to H₂ Sformation), to which is added about 7.2% CO. Since the fly ash thatremains and other components (including oxygen) of the gas stream do not"poison" the catalytic material of this process, it is effective toremove the sulfur dioxide as desired. It is contemplated that thecatalyst will work even better with gas streams, such as those from oilburning operations, where the O₂ /SO₂ ratio is more favorable and thelevel of fly ash is much lower.

In further aspects of the invention, the process of the presentinvention is considered applicable to other applications where the gasstream has a higher SO₂ content and a lower O₂ content, such as thosegas streams resulting from ore roasting, coal processing plants wherecoal is converted to gas and/or oil, or scrubbing systems where absorbedsulfide is oxidized to SO₂ to give a concentrated SO₂ -containing gasstream, etc. Typical gas concentrations contemplated here would be about3-20% SO₂, 1-5% O₂, a few % H₂ O, with the balance N₂. The SO₂ in such agas stream would be catalytically reduced, as taught herein, toelemental sulfur and any H₂ S formed, even in appreciable amounts, couldbe recycled through the catalytic reactor. Such H₂ S formation would notbe prohibitive since the bulk of the high concentration of the sulfurdioxide would be removed from the stream.

Reduction to elemental sulfur proceeds according to the known reactions:##EQU1## The important considerations in such processes relate to thereduction (and continued reduction) of the sulfur dioxide althoughoxygen, nitrogen oxides and other reducible components are present, thepossible reduction of sulfur dioxide to hydrogen sulfide in the presenceof water, the possible reduction to carbonyl sulfide by direct reactionbetween carbon monoxide and the sulfur dioxide, and the formation ofhydrogen sulfide and carbonyl sulfide by reaction of the gaseous sulfur,produced in the principal reduction step, with other components presentin the gas stream. In tests conducted to date with gas streams whichhave high SO₂ levels to which have been added or generated in situcarbon monoxide to increase the concentration thereof to not greaterthan the stoichiometric amount required to reduce all of the oxygen andsulfur present, it has been determined that the reduction of oxygen isfavored over the reduction of sulfur dioxide (in the presence ofoxygen), but the sulfur dioxide reduction is not excluded while oxygenis present; thus, in the presence or absence of oxygen, substantiallycomplete reduction of the sulfur dioxide to elemental sulfur can beeffected at temperatures below 700°C, generally between 450°C and 650°C;the presence of water at the elevated reaction temperatures does notlead to the formation of unacceptable hydrogen sulfide; and carbonylsulfide is not formed in appreciable amounts in the reduction process(unless the feed gas contains carbon monoxide in concentrations greaterthan the stoichiometric amount required to reduce all of the oxygen andsulfur dioxide). In addition, in the presence of water, the formation ofcarbonyl sulfide is further inhibited. The present process, therefore,as it pertains to gas streams having high SO₂ levels, affords distinctadvantages over known processes of which Applicant is aware since, in asingle stage (though multiple stages are contemplated), with atemperature requirement of less than 700°C, the sulfur dioxide isconverted to elemental sulfur with a conversion efficiency greater thanabout 90% while forming not greater than minimal quantities of carbonylsulfide and, quite unexpectedly, producing only low levels of hydrogensulfide under present operating conditions. This, in itself, is quitesurprising since thermodynamic calculations of the equilibria for thereactions involved predict that very little reduction to elementalsulfur will occur. Therefore, the results, as set forth above, would nothave been anticipated or expected.

Some hydrogen sulfide and/or carbonyl sulfide is formed with gas streamshaving low SO₂ and high water (>6%) concentrations, such as gas streamsobtained with coal or oil-burning processes. However, the formation ofsuch materials is within acceptable limits (considered to be much lessthan produced by other catalysts used for this purpose). In addition,activity of the catalyst is maintained for long periods of time, and thecatalyst is resistant to poisoning by oxygen and functions in thepresence of water vapor, thereby affording distinct advantages overother known catalysts used for the catalytic reduction of sulfur dioxidewith a reducing gas.

In the essential aspects of the process of the present invention, thesulfur dioxide-containing gas stream is heated from the deliverytemperature to a temperature in the range from about 450°C to about700°C, or higher, if desired, and then, if necessary, mixed withadditional carbon monoxide or hydrogen to provide a gaseous reactionmixture having the proper (or desired) stoichiometric balance betweenthe reducing gas and the sulfur dioxide (and other reducible materials).Carbon monoxide in extreme excess (i.e. >10% over the stoichiometricallyrequired amount) is to be avoided since it leads to the undesirableformation of carbonyl sulfide.

The sulfur dioxide/reducing gas gaseous stream is contacted with thecatalyst of the present invention in a first converter wherein thesulfur dioxide is converted to elemental sulfur and the carbon monoxideis oxidized to carbon dioxide and/or the hydrogen is oxidized to water.The elemental gaseous sulfur which is formed is then condensed from thegas stream as the gases are cooled. If desired, the gas stream can becontacted with a second batch of catalyst in one or more furtherconverters, after cooling to remove elemental sulfur (between eachconverter) to further increase the conversion efficiency of theprocessing system. Process parameters, materials of construction andtype and size of necessary process equipment can be determined byapplication of those chemical and process engineering principleswell-known in this field.

The catalyst is preferably treated with carbon monoxide at 700°C forabout 15-45 minutes, generally about 30 minutes, at the desired flowrates of nitrogen and carbon monoxide. This preferred step, which canbe, and generally is, conducted with the catalyst in place in thecatalytic reactor(s), has been found to raise the catalytic activity ofthe catalyst to its desired maximum prior to the time when it is firstcontacted by the sulfur dioxide-containing gas stream. This ensures thatthe catalytic conversion efficiency will be at its highest even duringthe first few hours of contact, whereas, in contrast, without such aprereduction step, there is a definite time interval, on the order ofhours, for the catalyst to reach maximum conversion efficiency for thegiven set of operating conditions. Thus, the prereduction step isdesirable to ensure maximum conversion of sulfur dioxide to elementalsulfur at all times.

Satisfactory conversion rates have been obtained with space velocitiesthrough the catalytic reactor(s) on the order of 2,000-36,000 volumes ofgas/volume of catalyst/hour, though both higher and lower spacevelocities, depending on the composition of the gas stream, arecontemplated.

A particular advantage of the catalyst and process of this invention isthat, upon temperature cycling from the desired operating temperature toa lower temperature followed by return to the desired operatingtemperature, the catalytic conversion returns to substantially theoriginal conversion rate. Thus, if there is an emergency shut-down ofthe system or catalytic reactor(s), or other lowering of the temperatureof the catalytic reactor(s), it does not become necessary to replace thecatalytic material. Instead, when ready, the catalytic reactor(s) can bereturned to the desired operating temperature and the catalytic materialwill perform substantially as well as before the temperature drop.

The catalyst of this invention can be pelletized by known techniques,such as by preparing an aqueous slurry, casting in the form of a thinsheet (1/8 inch thick) on an inert material, followed by drying andsintering at elevated temperatures. The sintered sheet is then brokeninto small pellets approximately 1/8 inch on an edge.

The catalyst of this invention can also be supported by known techniquesas, for example, by impregnating a suitable carrier material with anaqueous solution thereof, and subsequently drying and calcining theimpregnated material. Alternatively, the carrier material can besuitably loaded with the catalyst according to known dry impregnationtechniques. Suitable carrier materials include, for example, zirconia,thoria, magnesia, alumina, silica-alumina, and the like, especiallythose having extended surface areas. After catalyst impregnation, thecatalyst/support has more active sites per unit volume which promotesulfur dioxide reduction.

In an exemplary procedure, the carrier materials are sieved to -30/+60mesh, and impregnated with aqueous solutions of cobalt nitrate andeither yttrium or gadolinium nitrate, or other soluble salts, such as,for example, acetates, oxalates, and carbonates, to form, upon firing, acarrier impregnated with about 5.5% LnCoO₃. In a further exemplaryprocedure, unstabilized zirconia powders or yttrium oxide-stabilizedzirconia powders are mixed with the aforementioned nitrates (or othersalts) to prepare aqueous suspensions. The suspensions are extruded as1/8 inch diameter pellets, dried and then fired at temperatures betweenabout 900°C and 1100°C, preferably at about 900°C to about 1000°C, toyield fired pellets having a nominal 5 wt. % LnCoO₃ composition.Auxiliary agents, such as binders, e.g., camphor, lubricating andwetting agents, etc., can be added to the suspension to improve theextrusion or pellet forming process.

The catalysts of this invention having high surface area can also beprepared using a freeze drying technique. In this procedure, astoichiometric mixture of solutions of soluble salts of cobalt andeither yttrium and gadolinium are frozen, evaporated to remove the waterand vacuum decomposed to produce a mixture of cobalt oxide and eitheryttrium oxide or gadolinium oxides, as the case may be. This mixture canthen be fired in air to produce the desired material. Similar techniquescan be used to produce the catalysts of this invention on a suitablesupport, e.g., zirconia.

Since the pressure drop across a pellet type fixed catalyst bed can behigh and, therefore, will raise the operating cost of a catalyticreactor, honeycomb structures, such as cordierite honeycombs, can beused as supports for the catalytic material in the present invention aspressure drops therethrough are usually lower than with pellet typestructures.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE is a schematic flow diagram for the desulfurization offlue gases from a coal-burning power plant according to this invention.

DETAILED DESCRIPTION

Referring to the FIGURE there is shown a main power plant 10 whereinhigh sulfur content fuel is burned in the presence of air. A hightemperature ash precipitator 12, for example an electrostaticprecipitator, and, if necessary, other filtering means 14, are used toremove as much as possible (preferably all) of the particulate matterfrom the flue gas stream. If the flue gas stream contains excesshydrogen other than that limit considered desirable, a sacrificialcatalyst can be utilized in catalytic reactor 16 to remove such hydrogento prevent (or at least limit) the subsequent formation of hydrogensulfide. A carbon monoxide generator 18, such as a coal or oil gasifierthat may be as large as about 10% of the capacity of main power plant10, is used to furnish the carbon monoxide needed to reduce the sulfurdioxide and oxygen. Generator 18 is connected via line 20 to the fluegas stream 22 exiting from catalytic reactor 16 or, if reactor 16 isunnecessary, to the flue gas stream exiting from filter means 14. Thecatalytic reactor, containing the catalytic material of this invention,may be in a single stage or in multiple stages if interstage cooling isrequired or where a second stage is required to improve the overallefficiency of the sulfur removal process. As shown, flue gas stream 24containing sulfur dioxide, oxygen and carbon monoxide enters interstagecooler 26 and flows countercurrently to the gas stream exiting fromfirst stage catalytic reactor 28. After the gas stream has passedthrough cooler 26, catalytic reactor 28 and then cooler 26 again, thesulfur formed in reactor 28 is removed (as at 30) from the flowingstream before the gas stream enters second stage catalytic reactor 32.Since the carbon monoxide reacts exothermally with at least a part ofthe oxygen present, it is advantageous to recover this heat in heatremoval unit 34. The sulfur collected from the resultant gas stream 36in sulfur recovery unit 38 is combined with the sulfur removed at 30 andused as a valuable by-product of this process. After the resultant gasstream passes through precipitator 40 and compressor 42, it is exhaustedthrough stack 44. By-pass line 46 allows the gas stream to be directlyexited via stack 44 to allow, for example, for catalyst replacement,emergency shutdown of the reactor system, etc.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The following Examples are given to enable those skilled in this art tomore clearly understand and practice the present invention. They shouldnot be considered as a limitation upon the scope of the invention, butmerely as being illustrative and representative thereof.

EXAMPLE I

5.649 Grams of Y₂ O₃ and 4.075 grams of Co₂ O₃ were dry ground andblended using a mortar and pestle, and fired in air at 1100°C for 4hours in an uncovered platinum crucible. (It should be noted that thecobalt oxide used in the preparation of these materials actually existsas a mixture of CoO and Co₃ O₄, but this reagent grade cobalt oxide hasa cobalt assay which corresponds to 101% Co₂ O₃ ; accordingly, thecobalt oxide will be considered to be Co₂ O₃.) After the sample had beenoven-cooled to room temperature, it was removed from the furnace,reground with mortar and pestle, and refired at 1100°C for an additional4 hours. After the second firing the sample was oven-cooled to roomtemperature, removed from the furnace, reground and sieved through a 325mesh screen to afford a material which is predominantly Y₂ O₃ with somecobalt oxides.

EXAMPLE II

The procedure of Example I is repeated using 9.063 grams of Gd₂ O₃ and4.075 grams of Co₂ O₃ to prepare Gd₂ O₃ . Co₂ O₃.

EXAMPLES III AND IV

In these Examples, a screening reactor system (described below) has beenutilized to test the relative catalytic activity of the materialsembraced by this invention. The system has been set to give a conversionefficiency of about 60% (instead of 100%) with the reference catalyst,thereby enabling the detection of still more effective catalystcompositions.

Three gases (N₂, CO, and SO₂) are fed to a stainless steel manifold.From the manifold the gases pass through a 3/8 inch diameter, 12 incheslong, 21 element stainless steel static mixer (Kenics Corp., Danvers,Mass.), then to a reactor which consists of a 15 inch tube surrounding a1/2 inch diameter, 18 inches long quartz tube having fitted joints atboth ends. The catalyst sits in the reactor 4 inches above the bottom ofthe furnace and is supported by a small amount of fiberfrax wool. Theamount of catalyst used is 0.5 grams. The effluent from the reactorsystem goes into a sulfur collector, a 1/2 inch diameter, 8 inch longpyrex tube with fitted joints at both ends. A 1/4 inch tube leads to a1/4 inch stainless steel millipore filter. From the filter, the effluentpasses to a Carle Automatic Sampling Valve and timer which injectssamples every 10 minutes into a gas chromatograph.

The data for various catalytic compositions embraced by this inventionwith flow rates of 12 ml./min. of SO₂, 24 ml./min. of CO, and 84ml./min. of N₂ (catalyst volume = 0.59 cm³ ; contact time = 0.29 second)is tabulated in Table I below.

                                      TABLE I                                     __________________________________________________________________________                                  MAXIMUM                                                               TEMPERATURE                                                                           COS PRO-                                                              AT WHICH NO                                                                           DUCTION                                                                             % SO.sub.2                                                      REACTION                                                                              AT LOW                                                                              REMOVED                                   EXAMPLE                                                                             FORMULA PREPARATION                                                                           OCCURS  TEMP. AT 700°C                           __________________________________________________________________________    III   Y.sub.2 O.sub.3 .                                                                     See Ex. I                                                                             380°C                                                                          --    67%                                             Co.sub.2 O.sub.3                                                        IV    Gd.sub.2 O.sub.3.       5% at                                                 Co.sub.2 O.sub.3                                                                      See Ex. II                                                                            470°C                                                                          470°C                                                                        50%                                       __________________________________________________________________________

The reference catalyst has been shown to have catalytic conversionefficiencies on the order of 90% or greater under appropriatecondidtions and with properly constituted gas streams. Accordingly, 67%SO₂ removal for Y₂ O₃ . Co₂ O₃ under conditions which are pre-set togive 60% SO₂ removal with the reference catalyst is indicative that Y₂O₃ . Co₂ O₃ is at least as good as the reference catalyst, and possiblyslightly better, and that comparable catalytic conversion effienciesshould be attainable therewith. Thus, Y₂ O₃ . Co₂ O₃ is the preferredcatalytic material of this invention.

In certain instances where the said gas stream has a compositiondifferent from that set forth above or used in the Examples, thecatalytic conversion efficiency may be on the order of 75% or so.However, under appropriate conditions and with properly constituted gasstreams, conversion efficiencies on the order of 90% can be obtained.

While the present invention has been described with reference tospecific embodiments thereof, it should be understood by those skilledin this art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention. In addition, many modifications can be made to adapt aparticular situation, material or composition of matter, process,process step or steps, or then-present objective to the spirit of thisinvention without departing from its essential teachings.

What is claimed is:
 1. A process for removing sulfur dioxide from a gasstream containing sulfur dioxide comprising passing a gas streamcontaining sulfur dioxide and a sufficient amount of carbon monoxide orhydrogen to reduce at least a portion of said sulfur dioxide toelemental sulfur through a reaction chamber charged with a material ofthe formula Ln₂ O₃ . Co₂ O₃, where Ln is either Y or Gd, tocatalytically produce at a sufficiently elevated temperature a productstream containing elemental sulfur and carbon dioxide or water, andthereafter removing said elemental sulfur from said product stream. 2.The process of claim 1 wherein the temperature in said reaction chamberis in the range of from about 450°C to about 700°C.
 3. The process ofclaim 1 wherein said material is Y₂ O₃ . Co₂ O₃.
 4. The process of claim1 wherein said material is Gd₂ O₃ . Co₂ O₃.
 5. The process of claim 1wherein said process is characterized by a sulfur dioxide removalefficiency greater than about 90%.
 6. The process of claim 1 whereinsaid process is characterized by a sulfur dioxide removal efficiencygreater than about 90% even in the presence of oxygen in said reactionchamber.
 7. The process of claim 1 wherein the production of saidproduct stream proceeds even in the presence of oxygen in said reactionchamber.
 8. The process of claim 1 wherein not greater than minimalamounts of hydrogen sulfide and carbonyl sulfide are produced during thecatalytic production of said elemental sulfur.
 9. The process of claim 1wherein said carbon monoxide or hydrogen in said gas stream is in anamount not greater than the stoichiometric amount thereof required forreduction of all oxidants in said gas stream.
 10. The process of claim 1wherein said carbon monoxide or hydrogen in said gas stream is within ±15% of the stoichiometric amount required for complete reduction of alloxidants in said gas stream.
 11. The process of claim 1 wherein aportion of said carbon monoxide or hydrogen in said gas stream isgenerated in situ.
 12. The process of claim 1 wherein a portion of saidcarbon monoxide or hydrogen in said gas stream is added thereto from anexternal source.
 13. A process for removing sulfur dioxide from a gasstream containing sulfur dioxide comprising adding carbon monoxide orhydrogen to a gas stream containing sulfur dioxide and oxygen to therebyprovide a gaseous reaction stream, the total amount of carbon monoxideor hydrogen in said gaseous reaction stream being approximately thestoichiometric amount required for reduction of all oxidants in saidgaseous reaction stream, heating said gaseous reaction stream to atemperature in the range from about 450°C to about 700°C, passing saidheated gaseous reaction stream through at least one reaction chambercharged with a material represented by the formula Ln₂ O₃ . Co₂ O₃,where Ln is either Y or Gd, to catalytically produce a product streamcomprising elemental sulfur, carbon dioxide or water, and not greaterthan minimal quantities of hydrogen sulfide and carbonyl sulfide, andthereafter remving said elemental sulfur from said product stream. 14.The process of claim 13 wherein said material is Y₂ O₃ . Co₂ O₃.
 15. Theprocess of claim 13 wherein said material is Gd₂ O₃ . Co₂ O₃.
 16. Theprocess of claim 13 wherein said gaseous reaction stream contains aminor concentration of oxygen, and the production of said elementalsulfur proceeds even in the presence of said oxygen in said gaseousreaction stream.
 17. The process of claim 13 wherein said carbonmonoxide or hydrogen in said gaseous reaction stream is within ± 15% ofthe stoichiometric amount required for complete reduction of alloxidants in said gaseous reaction stream.
 18. The process of claim 1wherein said material is supported on a magnesia carrier.
 19. Theprocess of claim 13 wherein said material is supported on a magnesiacarrier.
 20. The process of claim 1 wherein said material is supportedon a zirconia carrier.
 21. The process of claim 13 wherein said materialis supported on a zirconia carrier.